Some electronic devices or systems, such as cell phones, laptops, camera recorders and other mobile battery operated devices, may include low drop-out (LDO) voltage regulators to provide relatively precise and stable DC voltages. The LDO voltage regulators are configured to provide power to electrical circuits in the electronic devices/systems.
FIG. 1 shows a conventional LDO voltage regulator 100. The LDO voltage regulator 100 can include a pass device 102, an error amplifier 104, a reference voltage circuit 106 and a feedback circuit 108. The LDO voltage regulator 100 can convert an input voltage VIN to an output voltage VOUT at a predetermined level to serve as a power supply. The LDO voltage regulator 100 can further include a compensation circuit 130 to improve stability of the LDO voltage regulator 100.
However, the error amplifier 104 and the reference voltage circuit 106 are driven/powered by the input voltage VIN which may not be stable. Thus, the LDO voltage regulator 100 may have a relatively low power supply rejection ratio (PSRR). The power supply rejection ratio of a regulator is defined as the ratio of the change in supply voltage to the corresponding change in output voltage of the regulator. In addition, the gain of the error amplifier 104 may need to be high enough to compensate characteristic changes of the pass device 102 caused by the input voltage VIN variation.